It is common to coat a blue LED die with phosphor or quantum dots (QDs), then encapsulate the structure with a transparent polymer encapsulant, such as silicone, epoxy, or other polymer. The phosphor or QDs convert the blue light to one or more other wavelengths, and the combination of blue light leaking through the wavelength-conversion layer and the converted wavelength(s) can create a wide range of colors, including white light.
Many types of phosphor and QDs are air-sensitive, causing them to degrade when heated and exposed to the moisture in air.
The polymers conventionally used to encapsulate an LED die and the wavelength conversion material are inadequate when the flux and temperature reach beyond 2 W/cm2 and 80° C. An encapsulant for high brightness LEDs must also have good thermal conductivity to conduct the heat from the LED die to the ambient air. Conventional polymers do not have adequate thermal conductivity for a high brightness/high temperature LED die.
A new sealing technique is needed that hermetically seals phosphor or QDs overlying a high brightness LED die, where the technique also provides good thermal conductivity between the LED die and ambient air. The technique should incur relatively low cost and should be highly reliable. Preferably, for high brightness (i.e., high flux) LED dies, the hermetic seal should remain reliable at temperatures well above 80° C. and with a light flux up to 20 W/cm2, and the temperature of the phosphor or quantum dots should be kept below 130° C. to avoid degradation.